The shaft seal device shown in FIG. 6 is a known as a conventional lip seal-type shaft seal device (hereinafter referred to as “prior art;” e.g., see Patent Document 1).
The shaft seal device of the prior art has a cartridge 62 fitted into the internal periphery of a shaft hole 61 of a housing 60; a first seal lip 63 made of rubber material fitted onto the cartridge 62 in a non-bonded state; a case 64 fitted onto the first seal lip 63 in a non-bonded state; a second seal lip 65 made of resin material crimped onto and held by the case 64 and a backup ring 66 for supporting the second seal lip; and an adapter 67 fitted onto the cartridge 62 on a sealing fluid side L of the first seal lip 63.
The adapter 67 in the shaft seal device of the prior art has a cross-sectional shape that is substantially the shape of the letter “c,” and has a cylindrical external peripheral flange 68 that is formed parallel to the axial center, as shown in FIG. 6. The adapter 67 cannot be fitted into the cartridge 62 when the diameter of the external peripheral flange 68 is excessively greater than the inside diameter of a cylindrical part 69 of the cartridge 62, and conversely, the adapter readily dislodges from the cartridge when the inside diameter is excessively small. Therefore, the adapter 67 must be manufactured with rigorous dimensional precision.
There are cases in which the housing 60 is not modified and only the diameter of a shaft 70 is modified to, e.g., 12 mm to 8 mm. In such a case, the inside diameter dimension of the first seal lip 63, the case 64, the second seal lip 65, the backup ring 66, and other members must be reduced in correspondence to the diameter of the shaft 70, and the width of the first seal lip 63 and the like in the radial direction is increased. There is accordingly a problem in that when the adapter 67 shown in FIG. 6 is used in an unmodified manner, the portion pressed by the adapter 67 on a sealing fluid side L of the first seal lip 63 is narrowed, and when the assembly is set on the shaft 70, the first seal lip 63 moves in the shaft insertion direction and a gap is formed between the first seal lip 63 and the case 64. When an attempt is made to reduce the inside diameter dimension of the adapter 67 and to increase the width in the radial direction in order to adapt to such a problem, the first seal lip 63 is compressed by the adapter 67 to the atmosphere side A because the internal peripheral side of the adapter is attached so as to slightly slope to the atmosphere side when the adapter 67 is press-fitted to the cartridge 62, and there is a problem in that the inside diameter dimension of the first seal lip 63 changes and the seal function is negatively affected. Accordingly, the inside diameter dimension of the adapter 67 cannot be reduced to increase the width in the radial direction.
FIGS. 5(a) and 5(b) show experimental results for the case in which the adapter 67 of the prior art shown in FIG. 6 is used in a shaft seal device having a small shaft diameter. It is apparent that the width of the adapter 67 in the radial direction is small, the lip part of the first seal lip 63 is pulled by the shaft 70 to the sealing fluid side L, a gap 69 is formed between the first seal lip 63 and the case 64, and the first seal lip 63 is moved by assembly onto the shaft 70 when the adapter is assembled onto the shaft 70 of FIG. 5(a). On the other hand, FIG. 5(b) shows a state in which assembly has been completed and system pressure is applied to the sealing fluid side L, and it is apparent that the first seal lip 63 and the case 64 are brought into contact with each other due to the pressure, and the first seal lip 63 is moved by the system pressure in the direction of the atmosphere side A.
In this manner, in the shaft seal device of the prior art, the seal lip readily moves under the effect of assembly onto the shaft 70 and system pressure, and this becomes a cause of reduced sealing performance.